The present disclosure describes a special image obscurement device for a light source.
In live dramatic performances controlled lighting is often used to illuminate a performer or other item of interest. The illuminated area for live dramatic performance is conventionally a circular beam of light called a xe2x80x9cspot light.xe2x80x9d This spot light has been formed from a bulb reflected by a spherical, parabolic, or ellipsoidal reflector. The combination forms a round beam due to the circular nature of reflectors and lenses.
The beam is often shaped by gobos. FIG. 1 shows a light source 100 projecting light through a triangular gobo 108 to the target 105. The metal gobo 108 as shown is a sheet of material with an aperture 110 in the shape of the desired illumination. Here, that aperture 110 is triangular, but more generally it could be any shape. The gobo 108 restricts the amount of light which passes from the light source 100 to the imaging lenses 103. As a result, the pattern of light 106 imaged on the stage 105 conforms to the shape of the aperture 110 in the gobo 108.
Light and Sound Design, the assignee of this application, have pioneered an alternate approach of forming the gobo from multiple selected reflective silicon micromirrors 200. One such array is called a digital mirror device (xe2x80x9cDMDxe2x80x9d) where individual mirrors are controlled by digital signals. See U.S. Pat. No. 5,828,485 the disclosure of which are herein incorporated by reference. DMDs have typically been used for projecting images from video sources. Because video images are typically rectangular, the mirrors of DMDs are arranged in a rectangular array of rows and columns.
The individual mirrors 200 of a DMD are rotatable. Each mirror 200 is mounted on a bar 204 such that it can rotate in place around the axis formed by the bar 204. Using this rotation, individual mirrors 200 can be turned xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d to restrict the available reflective surface.
FIG. 2 shows an example of using a DMD 400 to project a triangular illumination by turning xe2x80x9coffxe2x80x9d some of the mirrors in the DMD 400. The surface of the DMD 400 exposed to a light source 402 comprises three portions. The individual mirrors which are turned xe2x80x9conxe2x80x9d (toward the light source 402) make up an active portion 404. In FIG. 4A, the active portion 404 is triangular. The individual mirrors which are turned xe2x80x9coffxe2x80x9d (away from the light source 402) make up an inactive portion 406. These pixels are reflected. The third portion is a surrounding edge 408 of the DMD 400. Each of these portions of the DMD 400 reflects light from the light source 402 to different degrees.
FIG. 3 shows a resulting illumination pattern 410 with the active area 404 inactive area 406 and cage 408.
The inventors recognize that light reflected from the inactive portion 406 of the DMD 400 generates a dim rectangular penumbra 418 area is surrounding the bright desired area 404. Light reflected from the edge 408 of the DMD 400 generates a dim frame area. The inventors recognized that this rectangular penumbra 418 is not desirable.
The inventors also recognized that a circular penumbra is much less noticeable in the context of illumination used in dramatic lighting.
Accordingly the inventors have determined that it would be desirable to have a device which would provide a circular illumination without a rectangular penumbra while using a rectangular arrayed device as an imaging surface. The present disclosure provides such capabilities.
This disclosure describes controlling illumination from a light source. The disclosed system is optimized for use with a rectangular, arrayed, selective imaging device.
In a preferred embodiment, a rotatable shutter with three positions is placed between a DMD and the imaging optical system. The first position of the shutter is a mask, preferably a circle, placed at a point in the optical system to be slightly out of focus. This circle creates a circular mask and changes any unwanted dim reflection to a circular shape. The second position of the shutter is completely open, allowing substantially all the light to pass. The third position of the shutter is completely closed, blocking substantially all the light from passing.
An alternate embodiment for blocking the rectangular penumbra by changing any penumbra to round uses an iris shutter placed between a DMD and increases optics. The iris shutter creates a variable aperture which ranges from completely closed to completely open. Intermediate settings include circles of varying diameter, resulting in similar projections as with the first position of the shutter embodiment.
Another alternate embodiment for blocking the rectangular penumbra by changing any penumbra to round uses two reflective surfaces. The first reflective surface is a DMD. The second reflective surface is preferably a light-sensitive reflective surface such as a polymer. If the light striking a portion of the reflective surface is not sufficiently bright, that portion will not reflect the full amount of that light.
By controlling the penumbra illumination surrounding the desired illumination, DMDs and other pixel-based rectangular elements can be used in illumination devices without creating undesirable rectangular penumbras.